The charter-bus crash that killed two and injured dozens outside Dallas on Thursday happened in the middle of an aggressive push by federal regulators to shutter unscrupulous carriers and ramp up safety inspections.

The Federal Motor Carrier Safety Administration has shut down more than a dozen private bus companies — nearly half of which it deemed "imminent hazards" — over the past couple months. Last week, the agency announced it was deploying a team of more than 50 safety investigators throughout the country to conduct a wider examination of "higher risk" carriers, including many small charter operations. The FMCSA also asked local police to join the crackdown by boosting traffic enforcement.

The inspection teams headed out into the field on April 1, with orders to target 250 companies with lackluster safety records, according to the American Bus Association, a trade group whose officials were briefed by federal authorities.

Among the carriers already shut down by the FMCSA was Fung Wah, a popular discount bus service between New York City and Boston that had a history of crashes and safety violations.

DOT Questions Cardinal Coach Lines

The company involved in Thursday morning's crash experienced only minor safety violations over the last two years. Special agents from the U.S. Department of Transportation showed up at the company's Grand Prairie office searching for the owner and bus company records. (AP photo)

(Published Thursday, April 11, 2013)

It's not clear whether the owner of the bus that wrecked Thursday, Cardinal Coach Line, would have been targeted in the crackdown had the crash not happened. According to FMCSA's online record system, Cardinal Coach Line was given a "satisfactory" safety rating in 2009. In the past two years, none of the company's five buses has been in a crash, the records say. But the company's two inspections over that period found violations that resulted in putting a bus and/or or a driver out of service.

Cardinal Coach Line's voicemail system was not accepting messages late Thursday, so a representative could not be reached for comment.

In a letter to bus companies last week, FMCSA head Anne Ferro said her agency had rolled out other safety initiatives in recent years, but she was not satisfied with the results.

"We continue to see an unacceptable number of bus companies and drivers operating unsafely, resulting in far too many crashes with devastating impacts," Ferro wrote.

Federal data don't show any dramatic increase in fatal bus crashes. But while the number of bus crashes hasn't changed much over the years, the crash rate has dropped significantly because there are so many more buses, and they log so many more total miles, according to a FMCSA report covering 1975 to 2010.

In 2009, bus fatalities hit their lowest point, with 221 crashes and 254 deaths, the report says. That number edged up in 2010 to 245 fatal crashes and 276 people killed.

The number of fatal crashes involving motorcoaches—including charters and tour buses—vary year by year, with no discernible trend, the report shows. In 2010, there were 36 fatal crashes involving motorcoaches, and 53 people killed.

The more likely explanation for the federal crackdown is a series of high-profile accidents in recent months. That includes the February crash of a tour bus in Southern California, in which eight people were killed and about three dozen were injured, and the December wreck of a charter bus in Oregon, in which nine people died.

Daniel Blower, a research scientist at the University of Michigan's Transportation Research Institute, said that motorcoaches are typically very safe, and the number of crashes involving them pale in comparison to those involving trucks and cars. But Blower said he agreed with the new federal scrutiny of small charters, who typically are not subject to rigorous inspections because they "operate on the fringe."

The following is a list of recent fatal bus crashes, and some of the worst bus crashes in U.S. history.

April 5, 2013: One adult was killed and dozens of children were hospitalized when a school bus slammed into a Jeep in Wadsworth, Ill.

March 16, 2013: A bus carrying the Seton Hill University women's lacrosse team veered off the Pennsylvania Turnpike and hit a tree, killing a pregnant coach, her unborn child and the driver. Three other passengers were hospitalized.

Feb. 3, 2013: A bus full of Mexican tourists returning to Tijuana from California crashed while descending a mountain road near the resort town of Big Bear, killing eight and injuring about three dozen.

Feb. 2, 2013: Thirty-five people were hurt when a charter bus carrying students who'd just completed a visit to Harvard University slammed into an overpass.

Jan. 10, 2013: A commuter bus bound for New York City slammed into a mini school bus in central New Jersey, injuring more than a dozen people; the school bus was not carrying any children.

December 2012: A charter bus skidded off a snowy, mountainous stretch of Interstate 84 in Oregon, killing nine.

August 2012: One woman was killed and more than three-dozen people were hurt when a charter bus crashed on an Illinois highway between Chicago and St. Louis.

March 2012: A school bus was hit by a truck at an intersection near Port Saint Lucie, Fla., killing one student and injuring 19 other passengers.

February 2012: A school bus was hit by a dump truck at an intersection in southern New Jersey, killing one girl and injuring 17 other students.

May 2011: Four passengers were killed in a motorcoach rollover on Interstate 95 in Caroline County, Va.

March 2011: A charter bus carrying people back to New York City from the Mohegan Sun Casino in Connecticut slammed into a roadside barrier on Interstate 95. Fifteen passengers died and 18 were hurt.

August 2008: A bus chartered by Vietnamese religious pilgrims drove off a highway overpass north of Dallas, killing 17 and injuring dozens more.

March 2007: A bus carrying members of the Bluffton University baseball team spun out of control and fell from an overpass, killing the driver, his wife and seven passengers. Twenty-eight other passengers were hurt.

November 2006: Four students were killed and 23 injured when a school bus went over the side of elevated roadway in Huntsville, Ala.

September 2005: Two-dozen elderly passengers died when their bus caught fire near Houston while fleeing from Hurricane Rita.

May 1999: A tour bus carrying people to a casino in Mississippi veered off a New Orleans highway, killing 22 and injuring 24.

July 1991: Seven people were killed when a bus full of Girl Scouts overturned in Palm Springs, Calif. Another 53 were hurt.

October 1995: Seven students died when their school bus was hit by a train in Fox River Grove, Ill.

May 1988: A church bus was hit by a drunken driver in Carrollton, Ky., killing 27 people and injuring 34.

May 1986: A tour bus plunged into the West Walker River in Mono County, Calif. Eighteen elderly passengers died.

May 1985: A school bus was one of four vehicles involved in a collision near Snow Hill, N.C., in which six students and one driver died. Two dozen people were hurt.

June 1980: A tour bus from Texas careened off a curvy road and fell down a ravine in northern Arkansas, killing 22 and injuring 19.

May 1976: A bus carrying a California high school chorus drove off an exit ramp and fell 30 feet, landing upside down and killing 29 students.

February 1958: A school bus purged into the Big Sandy River near Prestonsburg, Ky., killing 26 students and the driver.